Export usages as docopt

[fenollp]

(Opening this to track but I'll probably end up implementing this myself.)

I love explainshell and I love docopt.org. I wish there was a docopt repo of many common commands so docopt adoption and usage would grow faster.
This repo does the dirty work of making sense of many/various manpages so they can be indexed and matched against an actual call.

I suggest to store these parsed manpages as docopt usage strings and to use docopt machinery to match the call.

• Matching comes for free
• This can help grow docopt.org's documentation
• Programs that use docopt can be added to the index instantly

If matching needs optimizing, one could also just provide an API that, given a command or a call, gives back a docopt usage string for that command.

[idank]

I'd be scared of tying a generic tool like explainshell to the format of a particular tool. I also wouldn't be surprised if some evil command arguments weren't expressible in docopt.

I do think explainshell needs an internal for its index though, I'm just not sure this is the right one.